Power consumption reduction in medical devices employing multiple supply voltages and clock frequency control

ABSTRACT

Power consumption in medical devices is reduced through the operation of circuits at clock speeds of lower levels to adequately complete desired functions during predetermined time periods (e.g., blanking interval, upper rate interval, etc.) just-in-time prior to subsequent required functional processes; by providing supply voltages tailored for various circuits of an integrated circuit; by operating two or more circuits of an integrated circuit at different clock frequencies; by changing the supply voltage level “on the fly” as required by specific circuit timing functions required for various circuitry based on clock frequencies used to control operation of such circuitry; and/or by tailoring back gate bias or adjusting back gate bias “on the fly” for circuits based on the supply voltage level applied to the circuits.

CLAIM TO PRIORITY AND REFERENCE TO RELATED APPLICATION

[0001] This application is a Continuation-In-Part, and claims priorityand other benefits from the filing date, of U.S. Patent Appin. Ser. No.09/067,881 for “Power Consumption Reduction in Medical Devices UsingMultiple Supply Voltages and Clock Frequency Control” to Thompson, filedApr. 29, 1998, hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

[0002] The present invention relates to power consumption of integratedcircuit designs such as circuits used in medical devices, particularlyimplantable devices. More particularly, the present invention pertainsto providing adjustable clock control and/or multiple supply voltagelevels for operation of such circuits.

BACKGROUND OF THE INVENTION

[0003] Various devices require operation with low power consumption. Forexample, hand-held communication devices require such low powerconsumption and, in particular, implantable medical devices require lowpower capabilities. With respect to implantable medical devices, forexample, microprocessor-based implantable cardiac devices, such asimplantable pacemakers and defibrillators, are required to operate witha lower power consumption to increase battery life and device longevity.

[0004] Generally, such low power devices are designed usingcomplementary metal oxide semiconductor (CMOS) technology. CMOStechnology is generally used because such technology has thecharacteristic of substantially zero “static” power consumption.

[0005] Power consumption of CMOS circuits consists generally of twopower consumption factors, namely “dynamic” power consumption and staticpower consumption. Static power consumption is only due to currentleakage as the quiescent current of such circuits is zero. Dynamic powerconsumption is the dominant factor of power consumption for CMOStechnology. Dynamic power consumption is basically due to the currentrequired to charge internal and load capacitances during switching, i.e.the charging and discharging of such capacitances. Dynamic power (P) isequal to: {fraction (1/2)}CV _(DD) ²F, where C is nodal capacitance, Fis the clock or switching frequency, and V_(DD) is the supply voltagefor the CMOS circuit. As can be seen from the formula for calculatingdynamic power (P), such dynamic power consumption of CMOS circuits isproportional to the square of the supply voltage (V_(DD)). In addition,dynamic power (P) is proportional to the switching or clock frequency(F).

[0006] In accordance with the formula for dynamic power consumption, ithas been effective conventionally in CMOS integrated circuit designs toscale down the supply voltage for an entire device (e.g. hybrid) orintegrated circuit (IC), i.e., operate the circuit at low supplyvoltages, to reduce power consumption for such designs. For example, inthe MEDTRONIC SPECTRAX® product of circa 1979, IC circuitry was poweredby one lithium iodine (as opposed to the two cells employed in the priorart). This reduced the supply voltage to 2.8 volts from 5.6 volts, thusreducing overhead current. Voltages required to be greater than 2.8volts were generated by a voltage doubler, or alternatively by a chargepump (e.g., output pacing pulses). In the MEDTRONIC SYMBIOS® product ofcirca 1983, for example, logic circuitry was powered by a voltageregulator controlling the IC supply voltage to a “sum of thresholds”supply. This regulator provided a supply to the IC (i.e., V_(DD)) ofseveral hundred millivolts above the sum of the n-channel and p-channelthresholds of the CMOS transistors making up the IC. This regulator wasself calibrating regarding manufacturing variations of the transistorthresholds.

[0007] Other devices reduced power consumption in other manners. Forexample, various device designs have shut-down analog blocks and/orshut-off clocks to logic blocks not being used at particular times,thereby reducing power. Microprocessor based devices have historicallyused a “burst clock” design to operate a microprocessor at a very highclock rate (e.g., generally 500-1000 Kilohertz (KHz)), for relativelyshort periods of time to gain the benefit of a “duty cycle” to reduceaverage current drain. A much lower frequency clock (e.g., generally 32KHz) is used for other circuitry and/or the processor when not in thehigh clock rate mode, i.e., burst clock mode. Many known processor basedimplanted devices utilize the burst clock technique. For example,implanted devices available from Medtronic, Vitatron, Biotronic, ELA,Intermedics, Pacesetters, InControl, Cordis, CPI, etc., utilize burstclock techniques. A few illustrative examples which describe the use ofa burst clock are provided in U.S. Pat. No. 4,561,442 to Vollmann etal., entitled “Implantable Cardiac Pacer With DiscontinuousMicroprocessor Programmable Anti Tachycardia Mechanisms and Patient DataTelemetry,” issued Dec. 31, 1985; U.S. Pat. No. 5,022,395 to Russie,entitled “Implantable Cardiac Device With Dual Clock Control ofMicroprocessor,” issued Jun. 11, 1991; U.S. Pat. No. 5,388,578 to Yomtovet al., entitled “Improved Electrode System For Use With An ImplantableCardiac Patient Monitor,” issued Feb. 14, 1995; and U.S. Pat. No.5,154,170 to Bennett et al., entitled “Optimization for Rate ResponsiveCardiac Pacemaker,” issued Oct. 13, 1992.

[0008]FIG. 1 illustrates graphically energy/delay versus supply voltagefor CMOS circuits such as CMOS inverter 10 shown in FIG. 2 forillustrative purposes. Inverter 10 is provided with a supply voltage,V_(DD), which is connected to the source of a PMOS field effecttransistor (FET) 12. PMOS FET 12 has its drain connected to the drain ofan NMOS FET 14 whose source is connected to ground. In thisconfiguration, an input V_(i) applied to both the gates of FETs 12, 14is inverted to provide output V_(o). Simply stated, one clock cycle, orlogic level change, is used to invert the input V_(i) to V_(o).

[0009] As shown in FIG. 1, the circuit logic delay increases drasticallyas the supply voltage is reduced to near one volt, as represented bydelay line 16 and energy/delay line 18. As such, reducing of the supplyvoltage (V_(DD)) continuously to lower levels is impractical because ofthe need for higher supply voltages when higher frequency operation isrequired. For example, generally CMOS logic circuits must periodicallyprovide functionality at a higher frequency, e.g., burst clockfrequency. However, as the supply voltage (V_(DD)) is decreased, suchenergy consumption is reduced by the square of the supply voltage(V_(DD)) as is shown by energy consumption line 20. Therefore, speedrequires a higher supply voltage (V_(DD)) which is in direct conflictwith low power consumption.

[0010] Other problems are also evident when lower supply voltages(V_(DD)) are used for CMOS circuit designs. When a lower supply voltageis selected, static leakage current losses may arise, particularly atlower frequencies, due to increased static leakage current losses.

[0011] Various techniques for reducing power consumption in devices areknown in the art, some examples of which may be found in the referenceslisted in Table 1 below. TABLE 1 Patent No. Inventor Issue Date4,031,899 Renirie 28 Jun. 1977 4,460,835 Masuoka 17 Jul. 1984 4,561,442Vollmann et al. 31 Dec. 1985 4,791,318 Lewis et al. 13 Dec. 19885,022,395 Russie 11 Jun. 1991 5,154,170 Bennett et al. 13 Oct. 19925,185,535 Farb et al. 9 Feb. 1993 5,388,578 Yomtov et al. 14 Feb. 19955,610,083 Chan et al. 11 Mar. 1997

[0012] All references listed in Table 1 herein above are herebyincorporated by reference in their respective entireties. As those ofordinary skill in the art will appreciate readily upon reading theSummary of the Invention, Detailed Description of the Embodiments, andclaims set forth below, at least some of the devices and methodsdisclosed in the present application, including those disclosed in thereferences listed in Table 1 hereinabove, may be modified advantageouslyin accordance with the teachings of the present invention.

SUMMARY OF THE INVENTION

[0013] The present invention has certain objects. That is, variousembodiments of the present invention provide solutions to one or moreproblems existing in the prior art respecting circuitry design havinglower power consumption, particularly with respect to implantablemedical devices. Those problems include: CMOS, CML, SOS, SOI, BICMOS,PMOS and/or NMOS circuits having too large of a dynamic powerconsumption which reduces battery life; the inability to utilize lowvoltage supply levels effectively: lack of ability to provide adequateprocessing capabilities such as high processing capabilities includingtelemetry uplink/downlink, morphology detection, initialization ofdevices, while still providing low processing capabilities such assensing intrinsic beats, pacing, low speed telemetry, with the desiredpower consumption; and the inability to provide circuit designs thatoperate at lower frequencies and thus lower power consumption as opposedto the use of higher speed clocks such as burst clocks.

[0014] In comparison to known techniques for reducing power consumptionin circuit designs, various embodiments of the present invention mayprovide one or more of the following advantages: reduced powerconsumption through the use of a lower voltage supply (V_(DD)); reducedpower consumption by decreased clock frequency for circuit designs;increased longevity of circuits, particularly implantable devicecircuitry; provide a potential reduction in product size; minimizestatic leakage current losses, i.e., static power consumption; providemulti-processor designs, DSP designs, and high performance processingdesigns with additional features/function opportunities due to theability to reduce power with respect to other “required” features andfunctions; and provide for substantial reduction in current drain.

[0015] Some embodiments of the invention include one or more of thefollowing features: operation of circuits to complete a desired function(generally completed in a predetermined number of clock cycles) at aclock speed of a lower or intermediate level to adequately completeprocessing just-in-time prior to the next required functional process;using substantially an entire predetermined time period (e.g., one basedon physiological events such as during a blanking interval, upper rateinterval, escape interval, refractory interval, and pulsegenerator/programmer handshake, etc.) to perform a function at a clockspeed such that the function is completed just prior to any nextrequired functional process; providing one or more voltage sources or avoltage source operable to provide one or more supply voltages tailoredfor various circuit functions of a single integrated circuit;operatively connecting a clock source to two or more circuits such thatdifferent circuits are operated at different clock frequencies,adjusting supply voltage levels connected to one or more circuits basedon the clock frequencies used for controlling operation of the circuits;adjusting back gate bias of a circuit based on the supply voltage levelapplied to the circuit; providing different supply voltage levels toprocessing circuitry depending upon the function being performed by theprocessing circuitry; operating processing circuitry at different clockfrequencies depending upon the function being performed by theprocessing circuitry; changing the supply voltage level “on the fly” asrequired by specific circuit timing functions required for variouscircuit or processing circuitry functionality based on clock frequenciesused to control operation of such circuitry; employing various ones orcombinations of the foregoing features in CMOS, CML (Current ModeLogic), SOS (Silicon on Sapphire), SOI (Silicon on Insulator), BICMOS,PMOS and/or NMOS circuitry.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a graphical illustration showing energy/delay versussupply voltage for CMOS circuit operation.

[0017]FIG. 2 shows a prior art CMOS inverter which is used as a buildingblock in many CMOS circuit designs.

[0018]FIG. 3 is a block diagram of a just-in-time clocking systemaccording to the present invention.

[0019] FIGS. 4A-4C show timing illustrations for use in describing thejust-in-time clocking system of FIG. 3.

[0020]FIG. 5 is a block diagram illustration of a multiple supplyvoltage system according to the present invention.

[0021]FIG. 6 is a block diagram illustrating a variable supply voltagesystem according to the present invention.

[0022]FIG. 7 is a block diagram of clock controlled processing circuitryaccording to the present invention.

[0023]FIG. 8 is a diagram illustrating an implantable medical device ina body.

[0024]FIG. 9 is a block diagram of the circuitry of a pacemaker for usein illustrating one or more embodiments of the present invention.

[0025]FIG. 10 is a schematic block diagram of an implantablepacemaker/cardioverter/defibrillatcr (PCD) for use in illustrating oneor more embodiments of the present invention.

[0026]FIG. 11 is a schematic block diagram illustrating a variableclock/variable supply voltage digital signal processing system accordingto the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The present invention is first generally described with referenceto FIGS. 3 through 7. Thereafter, the present invention is describedwith reference to illustrative configurations of implantable medicaldevices shown in FIGS. 8 through 11.

[0028]FIG. 3 shows a general block diagram of just-in-time clock system30. Just-in-time clock system 30 includes integrated circuit 32 andclock source 34. Integrated circuit 32 includes a plurality of circuitsC1-Cn. Each circuit when operable is capable of performing one or morecircuit functions. A function is defined as any operation perform on oneor more inputs in a plurality of cycles resulting in an output.Generally, the functions performed by the various circuits C1-Cn areperformed in a predetermined number of clock cycles. Clock source 34 isoperable for providing clock signals at a plurality of clock frequenciesgenerally shown as clock1-clockn.

[0029] Circuits C1-Cn of integrated circuit 32 may include discretefunction circuits (i.e., logic circuits for operating upon one or moreinputs to implement a particular function to provide one or more outputstherefrom), such as circuits operating on one input from a sensor toprovide a representative signal to further functional circuitry,transceiver circuitry, conversion circuitry, etc. Further, circuitsC1-Cn may be data processing circuitry capable of performing multiplefunctions under program control or such circuits C1-Cn may implementfirmware (software) functions/routines that must complete prior to somesucceeding event or prior to the start of the next function. Forexample, as described further herein with respect to illustrativeembodiments of implantable medical devices, such circuits may includedigital signal processing circuits, circuitry used for telemetryuplink/downlink, morphology detection circuitry, arrhythmia detectioncircuitry, monitoring circuitry, pacing circuitry, microprocessors, etc.

[0030] The functions performed by each of the circuits C1-Cn aretypically required to be completed in a particular time period prior toa next functional process being undertaken. For example, one logiccircuit may perform a function in a predetermined time period to providean output required by another circuit, or for example, a function mayneed to be performed by processing circuitry during a particular periodof time due to the need for other processing to be performed by suchprocessing circuitry. For example, in an implantable medical device,processing to complete a particular function may need to be performed ina portion of a particular time interval such as a blanking interval, anupper rate interval, an escape interval, or refractory interval of acardiac cycle, or further, such as during a pulse generator/ programmerhandshake.

[0031] Clock source 34 may be configured in any manner for providingclock signals at a plurality of frequencies. Such a clock source mayinclude any number of clock circuits wherein each provides a singleclock signal at a particular frequency, the clock source 34 may includeone or more adjustable clock circuits for providing clock signals over acontinuous range of clock frequencies, and/or the clock source 34 mayinclude a clock circuit that is operable to provide clock signals atdiscrete clock frequencies as opposed to over a continuous range. Forexample, the clock source 34 may include oscillators, clock dividers,timers, clock control circuitry or any other circuit elements requiredfor providing clock signaling according to the present invention.Preferably, clock source 34 is configured as a continuously oscillatinglow frequency clock and a controllable on/off higher frequency clock.

[0032] Just-in-time controllable clock operation of the just-in-timeclocking system 30 of FIG. 3 shall be described with reference to FIGS.4A-4C. As shown in FIG. 4A, time period (x) represents the time periodin which a circuit, e.g., one of circuits C1-Cn, is required to completeone or more functions. The same time period (x) is shown in FIG. 4B. Thetime period x may be equated to any number of different time periods.For example, the time period may be the amount of time a processingcircuit has to perform a particular detection function due to the needfor a detection output by a certain point in time, may be a time periodrequired to complete a particular function by a certain logic circuit soas to provide a timely output to a digital signal processing circuit,may be a time period to complete a firmware (software) routine, etc.Further, for example, the time period x may correspond to a cardiaccycle or a part thereof.

[0033] As shown in FIG. 4B, according to conventional processing,circuit functions were typically performed at a burst cycle frequencyand, as such, the function performed required a time period 60.Therefore, only a small amount of time (i.e., time period 60) of theentire time period x was used to perform the one or more functionsrequiring n cycles of time to complete. In such a case, conventionally,such burst clocks were at a substantially high clock rate, e.g.,500-1000 KHz, for such short periods of time to gain the benefit of a“duty cycle” to reduce average current drain. However, such high clockrates may not be required for carrying out such functions, or allfunctions.

[0034] With just-in-time clocking according to the present invention, asshown in FIG. 4A, substantially the entire time period x is used toperform the one or more functions which are completed in n cycles. Inother words, the clock frequency, e.g., one of clock1-clockn, for thecircuit performing the one or more functions during the time period x isset such that the one or more functions are completed in the maximumtime available for performing such functions, i.e., the clock frequencyis at its lowest possible value In other words, a lower frequency clockis used such that the one or more functions are performed just-in-timefor other circuit or routine functionality to be performed. In such ajust-in-time manner, the clock frequency used to control the performanceof such functions by the particular CMOS, CML, SOS, SOI, BICMOS, PMOSand/or NMOS type of circuitry is lowered resulting in reduced powerconsumption by the circuitry. That is, according to the calculations ofdynamic power, the lower frequency results in proportional powerreduction. With the lowering of the clock frequency, the integratedcircuit 32 including the various circuits C1-Cn can be designed tooperate at a lower frequency, e.g., as opposed to burst frequency, andalso at various other frequencies depending upon need.

[0035] Preferably, as used herein, use of the substantially entirepredetermined period of time may result in a completion of the one ormore functions being performed prior to the end of the time period x asis represented by remainder time periods 55 in FIG. 4A. This remaindertime period 55, for example, is preferably near 0 seconds.

[0036]FIG. 4C shows an illustrative timing example for processingcircuitry which performs multiple functions. For example, the cardiaccycle of a patient is represented in FIG. 4C as time period x. Duringtime period 71, i.e., during a QRS complex of the cardiac cycle, highspeed processing is performed at a high clock frequency relative to alower clock frequency used to control operation of the processingcircuitry during time period y. During the time period y, when theprocessing circuitry is operated at a lower clock frequency, such lowerclock frequency may be set such that the functions performed during zcycles are performed in substantially the entire maximum time periodavailable for such processing, i.e., time period y. Once again, a smallremainder time period 75 of the cardiac cycle time period x may exist.Such time period may be, for example, in the range of about 1.0millisecond to about 10.0 milliseconds when the cardiac cycle is in therange of about 400 milliseconds to about 1200 milliseconds.

[0037]FIG. 5 shows a general block diagram of a multiple supply voltagesystem 100 wherein one or more supply voltages are available andtailored for application to various circuits in an IC. The multiplesupply voltage system 100 includes integrated circuit 102 and supplyvoltage source 106. Integrated circuit 102 includes circuits C1-Cn.Supply voltage source 106 is operable for providing a plurality ofsupply voltages V1-Vn. Each supply voltage from supply voltage source106 is tailored to be applied to one or more circuits of circuits C1-Cn.As illustrated, supply voltage V1 is applied to circuit Cl, supplyvoltage V2 is applied to circuit C2 and C3, and so forth.

[0038] The tailoring of the supply voltages V1-Vn to the particularcircuits C1-Cn depends on the frequency at which the circuits C1-Cn arerequired to be operated. For example, and as previously described, thelogic delay of such CMOS, CML, SOS, SOI, BICMOS, PMOS and/or NMOScircuits C1-Cn increases drastically as the supply voltage is reduced tonear 1 volt. If such logic delay is tolerable, the supply voltageprovided to a particular circuit will drastically reduce the powerconsumption for that particular circuit as the energy is reduced inproportion to the square of the supply voltage (V_(DD)). However, ifsuch logic delay is not tolerable, for example, if the logic circuitperforms a function that must be completed within a particular period oftime, the reduction of the supply voltage (V_(DD)) applied to such acircuit will be limited depending upon the acceptable logic delay.However, the supply voltage V_(DD) for any particular circuit can bereduced as low as possible yet meet adequate speed requirements.

[0039] Integrated circuit 102 may include various different circuitsC1-Cn like those described with reference to FIG. 3. The supply voltagesource 106 may be implemented using a variety of components and mayinclude any number of voltage sources wherein each provides a singlesupply voltage level, may include one or more adjustable voltage sourcesfor providing supply voltage levels over a continuous range of levels,and/or may include a voltage source that is operable to provide discretesupply voltage levels as opposed to levels over a continuous range. Thesupply voltage source may include a voltage divider, a voltageregulator, a charge pump, or any other elements for providing the supplyvoltages V1-Vn. Preferably, the supply voltage source 106 is configuredas a charge pump.

[0040] Conventionally, supply voltage (V_(DD)) is generally in the rangeof about 3 volts to about 6 volts. Preferably, in accordance with thepresent invention, the supply voltages V1-Vn are in the range of about 1volt to about 3 volts dependent upon the CMOS, CML, SOS, SOI, BICMOS,PMOS and/or NMOS type of technology used.

[0041] With reduction in supply voltage (V_(DD)), threshold voltage(V_(T)) for the circuits is also reduced. For example, with supplyvoltages in the range of about 3 to about 6 volts, the threshold voltagefor CMOS, CML, SOS, SOI, BICMOS, PMOS and/or NMOS types of devices isgenerally in the range of about 0.8 volts to about 1.0 volt. Preferably,in implantable medical devices, lithium chemistries are utilized forimplantable batteries. Such lithium chemistries are generally in therange of about 2.8 volts to about 3.3 volts and generally the CMOS, CML,SOS, SOI, BICMOS, PMOS and/or NMOS circuitry has an associated thresholdvoltage of about 0.75. By reducing the supply voltages below 2.8, thevoltage thresholds for CMOS, CML, SOS, SOI, BICMOS, PMOS and/or NMOSdevices may be decreased to as low as about 0.2 volts to about 0.3volts.

[0042] Currently, there are various ultra low power logic designsoperating at a supply voltage as low as about 1.1, e.g., such as logicdesigns for microprocessors for a laptop and other portable productdesigns. By utilizing the tailored supply voltages V1-Vn, low power orultra low power logic designs may be used for at least some of thevarious circuits C1-Cn of integrated circuit 102. Other circuits mayrequire supply voltages of a higher nature. With use of lower thresholdlevels due to lower supply voltages, static power consumption lossesundesirably increase by several orders of magnitude.

[0043] Therefore, multiple supply voltage system 100 may furtheroptionally include back gate bias source 130 for providing back gatebias voltages BV1 -BVn to circuits C1-Cn of integrated circuit 102.Generally, the back gate bias voltages BV1-BVn are dependent upon thesupply voltage V1-Vn applied to the circuits C1-Cn to adjust thethreshold voltages for devices of circuits C1-Cn. For example, thethreshold voltage (VT) for the CMOS, CML, SOS, SOI, BICMOS. PMOS and/orNMOS devices of the circuit may be at a lower value by providing a backgate bias voltage to the particular circuits supplied with the lowersupply voltage. Further, for example, if circuit C1 is supplied with alower supply voltage V11, then a back gate bias voltage BV1 mayoptionally be applied to circuit C1 to adjust the threshold voltage(V_(T)) for the CMOS, CML, SOS, SOI, BICMOS, PMOS and/or NMOS devices toa higher threshold voltage (V_(T)) value. In this manner, static leakagecurrent losses can be minimized because the equivalent higher thresholdvoltage has been restored. Further, a broader range of supply voltagesis possible because the back gate adjustment allows a tailoring of thethreshold allowing high/low speed operation and eliminating the staticcurrent drain leakage.

[0044] The back gate bias voltage may be provided by, for example, afixed voltage source (i.e., a charge pump) connected to the back gatewell via a contact. Alternatively, an active body bias scheme wherebythe voltage source is selectable or adjustable over an appropriate rangemay be used.

[0045] Back gate voltages may be applied in any known manner. Forexample, the application of back gate bias voltages is described invarious patent references including U.S. Pat. Nos. 4,791,318 to Lewis etal., 4,460,835 to Masuoka, 5,610,083 to Chan et al., and U.S. Pat. No.5,185,535 to Farb et al., all incorporated by reference herein in theirrespective entireties.

[0046]FIG. 6 shows a general block diagram of a variable supplyvoltage/variable clock system 150 according to the present invention.The system 150 includes integrated circuit 152, clock source 156, supplyvoltage source 154, and clock/supply voltage interface 155. Supplyvoltage source 154 is operable for providing a plurality of supplyvoltages V1-Vn to a plurality of circuits C1-Cn of integrated circuit152. Further, the clock source 156 of system 150 is operable forproviding clock signals at a plurality of frequencies, clock1-clockn.Circuits C1-Cn are of a similar nature to those described with referenceto FIG. 3, the clock source 156 is similar to the clock source 34 asdescribed with reference to FIG. 3, and the supply voltage source 154 issimilar to the supply voltage source 106 as described with reference toFIG. 5. However, in the variable supply voltage/variable clock system150, a clock/voltage interface 155 is used to adjust the supply voltagesV1-Vn applied to the circuits C1-Cn “on the fly” as required by specifictiming functions required by the circuits C1-Cn.

[0047] As an illustrative example, circuit C1 may be a particular logiccircuit for performing one or more particular functions. However, suchfunctions may be required to be performed in a first time period at afirst clock frequency and during a different second time period at asecond clock frequency to perform such function within the allowed timeof the respective first and second time periods. In other words, onetime period is shorter than the other and, as such, the functions whichrequire performance over a certain number of cycles must be performed ata higher clock frequency if it is to be completed within a time periodthat is shorter than another time period. In such an example, accordingto the present invention, clock/voltage interface 155 detects the clocksignal applied to circuit C1 during the first time period in which thehigher frequency clock signal is used and accordingly provides supplyvoltage source 154 with a signal to select and apply a certain supplyvoltage corresponding to the higher clock frequency. Thereafter, whenthe lower clock frequency is applied to circuit C1 during the secondtime period, clock/voltage interface 155 senses the use of the lowerclock frequency and applies a signal to voltage supply source 154 forapplication of a certain supply voltage corresponding to the lower clockfrequency for application to circuit C1.

[0048] Further, for example, circuit C2 may be a CMOS, CML, SOS, SOI,BICMOS, PMOS and/or NMOS type of processor which may also have clockfrequency and corresponding supply voltage adjustments made “on thefly.” Such a system will be readily apparent from the discussion tofollow with reference to FIG. 7.

[0049]FIG. 7 shows a general block diagram of a clock controlledprocessing system 200 according to the present invention. The clockcontrolled processing system 200 includes processor 202 (e.g., a CMOS,CML, SOS, SOI, BICMOS, PMOS and/or NMOS type of microprocessor or CMOS,CML, SOS, SOI. BICMOS, PMOS and/or NMOS type of digital signalprocessor), clock source 204, supply voltage source 206. voltageregulator 212, regulator interface 210, clock control 208, and optionalback gate bias source 214. In a manner similar to that described withreference to FIG. 6, the supply voltage 206 applied to processor 202 ischanged “on the fly” as required by specific circuit timingrequirements.

[0050] Generally, processor 202 is operated under control of clocksource 204. Depending on the processing capability required, clocksource 204 may operate processor 202 at any one of a plurality of clockfrequencies. Such clock frequencies will be selected under the controlof clock control 208. Clock control 208 may be part of any timing andcontrol hardware and/or timing and control software used to controloperation of processor 202 as part of a larger system. For example, suchclock control may take the form of a digital controller/timer circuitfor performing timing control of an implantable medical device.

[0051] Processor 202 may perform any number of functions as appropriatefor the device in which it is used. High frequency processingcapabilities (i.e., about 250 KHz to about 10 MHz), low frequencyprocessing capabilities (i.e., about 1 Hz to about 32 KHz), andprocessing capabilities with regard to frequencies between such limitsare contemplated according to the present invention. For simplicitypurposes, clock control processing system 200 operation is describedwith reference to processor 202 performing only two different functions,each during a predetermined respective period of time. For example, withrespect to an implantable medical device such as a pacemaker, during thefirst period of time, a high processing function requiring a relativelyhigh clock frequency may include a function such as telemetryuplink/downlink, morphology detection, initialization, arrhythmiadetection, far-field R-wave detection, EMI detection, retrogradeconduction, etc. On the other hand, low frequency processing functionsmay include a function such as sensing intrinsic beats, pacing, lowspeed telemetry, transtelephonic data transfer, remote monitoring,battery checks, etc.

[0052] When processor 202 during a predetermined time is to perform highfrequency processing functions, a relatively high clock frequency, e.g.250 KHz to 10 MHz, may be supplied by clock source 204 for operation ofprocessor 202. Regulator interface 210 will detect the higher clockfrequency applied to processor 202 for operation during the highprocessing function and apply a control signal to voltage regulator 212for regulation of the supply voltage source 206. Supply voltage source206 is operable under control of voltage regulator 212 to provide asupply voltage within a predetermined range, preferably between about1.1 volts and about 3 volts. When a high clock frequency is used foroperation of processor 202 for high frequency processing functions,supply voltage source 206 generally applies a supply voltage in theupper range of the preferred supply voltages to the CMOS, CML, SOS, SOI,BICMOS, PMOS and/or NMOS devices of processor 202.

[0053] On the other hand, when processor 202 is to execute low frequencyprocessing functions during the predetermined periods of time, clockcontrol 208 signals clock source 204 to apply a lower frequency foroperation of processor 202. As such, regulator interface 210 detects thelower frequency being used to operate processor 202 and issues a controlsignal to voltage regulator 212 for regulation of supply voltage source206 such that a lower supply voltage in the lower end of the preferredrange of supply voltages is applied to the CMOS, CML, SOS, SOI, BICMOS,PMOS and/or NMOS devices of processor 202.

[0054] It will be recognized by those skilled in the art that anyintermediate processing capability may be achieved between the higherfrequency and the lower frequency capabilities described above and thatthe present invention is in no manner limited to processing at only twoclock frequencies and at two corresponding supply voltages. Rather,multiple levels of processing capability can be achieved according tothe present invention with associated clock frequencies andcorresponding supply voltages being applied to processor 202.

[0055]FIG. 4C illustrates one embodiment of the clock control processingsystem 200. As shown therein, during the overall cardiac cycle ofpredetermined time period x, a high frequency is used for controllingoperation of processor 202 during time period 71 of the cardiac cycletime period x, e.g., during processing of the QRS complex. Thereafter, alower clock frequency is used during time period y for controllingoperation of processor 202 to perform any of a number of other differentfunctions, such as cardiac event/EMI differentiation functions. Duringoperation of the processor 202 at the higher clock frequency during timeperiod 71, a higher supply voltage from supply voltage source 206 isapplied to the CMOS, CML, SOS, SOI, BICMOS, PMOS and/or NMOS devices ofprocessor 202. Likewise, during operation of the processor 202 at therelatively lower clock frequency, a lower supply voltage from supplyvoltage source 206 is applied to the CMOS or other types of devices ofprocessor 202 during time period y of the overall cardiac cycle timeperiod x.

[0056] Further, as shown in FIG. 7, an optional back gate bias 214 maybe used to dynamically adjust the threshold voltage (V_(T)) of CMOS,CML, SOS, SOI, BICMOS, PMOS and/or NMOS devices of processor 202 as afunction of the clock frequency applied to processor 202 by clock source204. The regulator interface 210 detects the clock frequency used tocontrol operation of processor 202 and controls the voltage level ofback gate bias 214 to be applied to the CMOS, CML, SOS, SOI, BICMOS,PMOS and/or NMOS devices of processor 202. The dynamic adjustment of thethreshold voltage may be implemented as an adjustable or selectablevoltage source utilizing, for example, a charge pump and a regulator.The back gate voltage and the “normal” gate voltage provide a gate biasor voltage to the transistor. By adjusting the back gate voltage, the“apparent” voltage is increased with a resultant reduction in leakagecurrent.

[0057]FIG. 8 is a simplified diagram of implantable medical device 260for which the present invention is useful. Implantable device 260 isimplanted in a body 250 near a human heart 264. lmplantable medicaldevice 260 is connected to heart 264 by leads 262. In the case wheredevice 260 is a pacemaker, leads 262 are pacing and sensing leads tosense electrical signals attendant to the depolarization andrepolarization of the heart 264 and provide pacing pulses in thevicinity of the distal ends thereof. Implantable medical device 260 maybe any implantable cardiac pacemaker such as those disclosed in U.S.Pat. Nos. 5,158,078 to Bennett et al., 5,312,453 to Shelton et al., orU.S. Pat. No. 5,144,949 to Olson, all hereby incorporated herein byreference in their respective entireties and which can all be modifiedaccording to the present invention.

[0058] Implantable medical device 260 may also be a pacemaker/cardioverter/defibrillator (PCD) corresponding to any of the variouscommercially-available implantable PCDs, one of which is summarilydescribed herein with reference to FIG. 10 and described in detail inU.S. Pat. No. 5,447,519. In addition to the PCD described in U.S. Pat.No. 5,447,519, the present invention may be practiced in conjunctionwith PCDs such as those disclosed in U.S. Pat. Nos. 5,545,186 to Olsonet al., 5,354,316 to Keimel, 5,314,430 to Bardy. 5,131,388 to Pless, or4,821,723 to Baker et a. all hereby incorporated herein by reference intheir respective entireties. Those devices may be employed using thepresent invention in that such devices may employ or be modified withcircuitry and/or systems according to the present invention.

[0059] Alternatively, implantable medical device 260 may be animplantable nerve stimulator or muscle stimulator such as thosedisclosed in U.S. Pat. Nos. 5,199,428 to Obel et al., 5,207,218 toCarpentier et al., or U.S. Pat. No. 5,330,507 to Schwartz, or animplantable monitoring device such as that disclosed in U.S. Pat. No.5,331,966 issued to Bennet et al., all of which are hereby incorporatedby reference herein in their respective entireties.

[0060] The present invention is believed to find wide application to anyform of electrical device which uses CMOS, CML, SOS, SOS, BICMOS, PMOS,and/or NMOS devices, and is further believed to be particularlyadvantageous where low power consumption is desired, particularly inimplantable medical devices.

[0061] At least some of the devices and methods disclosed in U.S. PatentAppln. Ser. No. 09/158,566 for “Cardiac Pacing System with ImprovedPhysiological Event Classification based on DSP” to Wohigemuth filedSep. 22, 1998 may also be advantageously modified in accordance with theteachings of the present invention. The foregoing '566 patentapplication is hereby incorporated by reference herein in its entirety.

[0062] In general, implantable medical device 260 includes ahermetically-sealed enclosure that includes an electrochemical cell suchas a lithium battery, CMOS, CML, SOS, SOI, BICMOS, PMOS and/or NMOScircuitry that controls device operations, and a telemetry transceiverantenna and circuit that receives downlinked telemetry commands from andtransmits stored data in a telemetry uplink to an external programmer.The circuitry may be implemented in discrete logic and/or may include amicrocomputer-based system with A/D conversion.

[0063] It is to be understood that the present invention is not limitedin scope to particular electronic features and operations of particularimplantable medical devices and that the present invention may be usefulin conjunction with various implantable devices. Further, the presentinvention is not limited in scope to implantable medical devicesincluding only a single processor but may be applicable tomultiple-processor devices as well.

[0064]FIG. 9 shows a block diagram illustrating the components of apacemaker 300 in accordance with one embodiment of the presentinvention. Pacemaker 300 has a microprocessor-based architecture.However, the illustrative pacemaker 300 of FIG. 9 is only one exemplaryembodiment of such devices and it will be understood that it could beimplemented in any logic-based, custom integrated circuit architecture,if desired, as can any microprocessor-based system.

[0065] In the illustrative embodiment of FIG. 9, pacemaker 300 is mostpreferably programmable by means of an external programming unit (notshown in the figures). One such programmer suitable for the purposes ofthe present invention is the commercially available Medtronic Model 9790programmer. The programmer is a microprocessor-based device whichprovides a series of encoded signals to pacemaker 300 by means of aprogramming head which transmits radio frequency (RF) encoded signals toantenna 334 of pacemaker 300 according to a telemetry system such as,for example, that described in U.S. Pat. No. 5,127,404 to Wyborny etal., the disclosure of which is hereby incorporated by reference hereinin its entirety. It is to be understood, however, that any programmingmethodology may be employed so long as the desired information istransmitted to and from the pacemaker.

[0066] Pacemaker 300 illustratively shown in FIG. 9 is electricallycoupled to heart 264 by leads 302. Lead 302 a including electrode 306 iscoupled to a node 310 in the circuitry of pacemaker 300 through inputcapacitor 308. Lead 302 b is coupled to pressure circuitry 354 ofinput/output circuit 312 to provide a pressure signal from sensor 309 tothe circuit 354. The pressure signal is used to ascertain metabolicrequirements and/or cardiac output of a patient Further, activity sensor351, such as a piezoceramic accelerometer, provides a sensor output toactivity circuit 352 of input/output circuit 312. The sensor outputvaries as a function of a measured parameter that relates to metabolicrequirements of a patient. Input/output circuit 312 contains circuitsfor interfacing to heart 264, to activity sensor 351, to antenna 334, topressure sensor 309 and circuits for application of stimulating pulsesto heart 264 to control its rate as a function thereof under control ofsoftware-implemented algorithms in microcomputer unit 314.

[0067] Microcomputer unit 314 preferably comprises on-board circuit 316that includes microprocessor 320, system clock circuit 322, and on-boardrandom access memory (RAM) 324 and read only memory (ROM) 326. In thisillustrative embodiment, off-board circuit 328 comprises a RAM/ROM unit.On-board circuit 316 and off-board circuit 328 are each coupled by acommunication bus 330 to digital controller/timer circuit 332.

[0068] According to the present invention, the circuits shown in FIG. 9are powered by an appropriate implantable battery supply voltage source301 (e g., a voltage source generally shown in FIGS. 1-7). For the sakeof clarity, the coupling of supply voltage source 301 to variouscircuits of pacemaker 300 is not shown in the figures. Further, thecircuits operable under control of a clock signal shown in FIG. 9 areoperated according to the present invention under clock source 338. Forthe sake of clanty, the coupling of such clock signals from the clocksource 338 (e.g., a clock source generally shown in FIGS. 1-7) to suchCMOS, CML, SOS, SOI, BICMOS, PMOS and/or NMOS circuits of pacemaker 300is not shown in the Figures.

[0069] Antenna 334 is connected to input/output circuit 312 to permituplink/downlink telemetry through RF transmitter and receiver unit 336.Unit 336 may correspond to the telemetry and program logic disclosed inU.S. Pat. No. 4,556,063 issued to Thompson et al., hereby incorporatedby reference herein in its entirety, or to that disclosed in theabove-referenced Wyborny et al. patent.

[0070] V_(REF) and bias circuit 340 generates a stable voltage referenceand bias currents for circuits of input/output circuit 312.Analog-to-digital converter (ADC) and multiplexer unit 342 digitizeanalog signals and voltages to provide “real-time” telemetryintracardiac signals and battery end-of-life (EOL) replacement function.A power on reset circuit 341 functions as a means to reset circuitry.

[0071] Operating commands for controlling the timing of pacemaker 300are coupled by bus 330 to digital controller/timer circuit 332. wheredigital timers and counters establish the overall escape interval ofpacemaker 300 as well as various refractory, blanking, and other timingwindows for controlling the operation of the peripheral componentsdisposed within input/output circuit 312.

[0072] Digital controller/timer circuit 332 is preferably coupled tosense circuitry 345 and to electrogram (EGM) amplifier 348 for receivingamplified and processed signals sensed by electrode 306 disposed on lead302 a. Such signals are representative of the electrical activity of thepatient's heart 264. Sense amplifier 346 of circuitry 345 amplifiessensed electrocardiac signals and provides an amplified signal to peaksense and threshold measurement circuitry 347. Circuit 347 in turnprovides an indication of peak sensed voltages and measured senseamplifier threshold voltages on path 357 to digital controller/timercircuit 332. An amplified sense amplifier signal is also provided tocomparator/threshold detector 40. Sense amplifier 332 may correspond tothat disclosed in U.S. Pat. No. 4,379,459 to Stein, which is herebyincorporated by reference herein in its entirety.

[0073] The electrogram signal provided by EGM amplifier 348 is employedwhen the implanted device 300 is being interrogated by an externalprogrammer (not shown) to transmit by uplink telemetry a representationof an analog electrogram of the patient's electrical heart activity.Such functionality is, for example, shown in U.S. Pat. No. 4,556,063 toThompson et al., previously incorporated by reference.

[0074] Output pulse generator and amplifier 350 provides pacing stimulito heart 264 through coupling capacitor 305 and electrode 306 inresponse to a pacing trigger signal provided by digital controller/timercircuit 332. Output amplifier 350 may correspond generally to the outputamplifier disclosed in U.S. Pat. No. 4,476,868 to Thompson. alsoincorporated by reference herein in its entirety. The circuits of FIG. 9may be CMOS, CML, SOS, SOI, BICMOS, PMOS and/or NMOS circuitry capableof operating according to the present invention, and include processor320, digital controller timer circuit 332, RAM 324, ROM 326, RAM/ROMunit 323 and ADC/Mux 342.

[0075]FIG. 10 is a functional schematic diagram from U.S. Pat. No.5,447,519 to Peterson. which shows an implantable PCD 400 in which thepresent invention may usefully be practiced. This diagram is anillustration to be taken only as an exemplary type of device in whichthe invention may be embodied, and not as limiting to the scope of thepresent invention. Other implantable medical devices as previouslydescribed having functional organizations wherein the present inventionmay be useful may also be modified in accordance with the presentinvention. For example, the present invention is also believed to beuseful in conjunction with implantable PCDs as disclosed in prior U.S.Pat. Nos. 4,548,209 to Wielders et al.; 4,693,253 to Adams et al.;4,830,006 to Haluska et al.; and U.S. Pat. No. 4,949,730 to Pless etal.; all of which are incorporated herein by reference in theirentireties.

[0076] Illustrative PCD 400 is provided with six electrodes 401, 402,404, 406, 408, and 410. For example, electrodes 401 and 402 may be apair of closely-spaced electrodes positioned in the ventricle of theheart 264. Electrode 404 may correspond to a remote, indifferentelectrode located on the housing of the implantable PCD 400. Electrodes406, 408, and 410 may correspond to large surface area defibrillationelectrodes located on leads to the heart 264 or epicardial electrodes.

[0077] Electrodes 401 and 402 are shown as hard-wired to the near field(i.e., narrowly spaced electrodes) R-wave detector circuit 419comprising band pass filtered amplifier 414, auto threshold circuit 416(for providing an adjustable sensing threshold as a function of themeasured R-wave amplitude), and comparator 418. Rout signal 464 isgenerated whenever the signal sensed between electrodes 401 and 402exceeds a sensing threshold defined by auto threshold circuit 416.Further, the gain on amplifier 414 is adjusted by pacer timer andcontrol circuitry 420. The sense signal, for example s used to set thetiming windows and to align successive waveshape data for morphologydetection purposes. For example, the sense event signal 464 may berouted through the pacer/timer control circuit 420 on bus 440 toprocessor 424 and may act as an interrupt for the processor 424 suchthat a particular routine of operations, e.g., morphology detection,discrimination functions, is commenced by processor 424.

[0078] Switch matrix 412 is used to select available electrodes undercontrol of processor 424 via data/address bus 440 such that theselection includes two electrodes employed as a far field electrode pair(i.e., widely spaced electrodes) in conjunction with atachycardia/fibrillation discrimination function (e.g., a function todiscriminate between tachycardia, i.e., an abnormally fast heart rate,and fibrillation, i.e., uncoordinated and irregular heartbeats, so as toapply an appropriate therapy). Far field EGM signals from the selectedelectrodes are passed through band pass amplifier 434 and intomultiplexer 432, where they are converted to digital data signals byanalog to digital converter (ADC) 430 for storage in random accessmemory 426 under control of direct memory access circuitry 428. Forexample, a series of EGM complexes for several seconds may be performed.

[0079] According to the present invention, the circuits shown in FIG. 10are powered by appropriate implantable battery supply voltage source 490(e.g., a voltage source generally shown in FIGS. 1-7 For the sake ofclarity, the coupling of supply voltage source 490 to various circuitsof PCD 400 is not shown in the figures. Further, the circuits operableunder control of a clock signal shown in FIG. 10 are operated accordingto the present invention under clock source 491. For the sake ofclarity, the coupling of such clock signals from the clock source 491(e.g., a clock source generally shown in FIGS. 1-7) to such CMOS, CML,SOS, SOI, BICMOS, PMOS and/or NMOS circuits of PCD 400 is not shown inthe Figures.

[0080] The occurrence of an R-wave sense event or detect signal Rout 464is communicated to processor 424 to initiate morphology analysis onwaveforms by processor 424 for use in selection of a theraby for heart264. For example, the processor may calculate the cumulativebeat-to-beat variability of heart 264, time intervals separating R-wavesense events, and various other functions as set out in numerousreferences including any of the references already listed herein andvarious other references with regard to implantable PCDs.

[0081] Other portions of PCD 400 of FIG. 10 are dedicated to theprovision of cardiac pacing, cardioversion, and defibrillationtherapies. With regard to cardiac pacing, the pacer timing/controlcircuit 420 includes programmable digital counters which control thebasic timing intervals associated with cardiac pacing, including thepacing escape intervals, the refractory periods during which sensedR-waves are ineffective to restart timing of escape intervals, etc. Thedurations of such intervals are typically determined by processor 424and communicated to pacer timer/control circuit 420 via address/data bus440.

[0082] Further, under control of processor 424, pacer timing/controlcircuit also determines the amplitude of such cardiac pacing pulses andpace out circuit 421 provides such pulses to the heart.

[0083] In the event that a tachyarrhythmia (i.e., tachycardia) isdetected, and an anti-tachyarrhythmia pacing therapy is desired,appropriate timing intervals for controlling generation ofanti-tachycardia pacing therapies are loaded from processor 424 intopacer timing and control circuitry 420. Similarly, in the event thatgeneration of a cardioversion or defibrillation pulse is required,processor 424 employs the counters and timing and control circuitry 420to control timing of such cardioversion and defibrillation pulses.

[0084] In response to detection of fibrillation or a tachycardiarequiring a cardioversion pulse, processor 424 activatescardioversion/defibrillation control circuitry 454, which initiatescharging of the high voltage capacitors 456, 458, 460 and 462 viacharging circuit 450 under control of high voltage charging line 452.Thereafter, delivery of the timing of the defibrillation orcardioversion pulse is controlled by pacer timing/control circuitry 420.Various embodiments of an appropriate system for delivering andsynchronization of cardioversion and defibrillation pulses, andcontrolling the timing functions related to them is disclosed in moredetail in U.S. Pat. No. 5,188,105 to Keimel, which is incorporatedherein by reference in its entirety. Other such circuitry forcontrolling the timing and generation of cardioversion anddefibrillation pulses is disclosed in U.S. Pat. No. 4,384,585 to Zipes,U.S. Pat. No. 4,949,719 to Pless et al., and in U.S. Pat. No. 4,375,817to Engle et al., all incorporated herein by reference in theirentireties. Further, known circuitry for controlling the timing andgeneration of anti-tachycardia pacing pulses is described in U.S. Pat.No. 4,577,633 to Berkovits et al., U.S. Pat. No. 4,880,005 to Pless etal., U.S. Pat. No. 4,726,380 to Vollmann et al., and U.S. Pat. No.4,587,970 to Holley et al., all of which are incorporated herein byreference in their entireties.

[0085] Selection of a particular electrode configuration for delivery ofthe cardioversion or defibrillation pulses is controlled via outputcircuit 448 under control of cardioversion/defibrillation controlcircuit 454 via control bus 446. Output circuit 448 determines which ofthe high voltage electrodes 406, 408 and 410 will be employed indelivering the defibrillation or cardioversion pulse regimen.

[0086] The components of PCD 400 of FIG. 10 may be CMOS, CML, SOS, SOI,BICMOS, PMOS and/or NMOS circuitry capable of operation according to thepresent invention include processor 424, control circuits 420 and 454,RAM 426, DMA 428, ADC 430, and multiplexer 432.

[0087] According to the present invention, pacemaker 300 illustrated inFIG. 9 and PCD 400 illustrated in FIG. 10 may both be implemented inaccordance with the generalized embodiments previously described hereinwith reference to FIGS. 1-7. First, for example, with respect topacemaker 300 of FIG. 9, the voltage supply source 301 of pacemaker 300may be implemented in a manner previously described with reference toFIGS. 1-7 and, likewise, clock source 338 of pacemaker 300 may beimplemented in such a manner as described with reference to FIGS. 1-7.Likewise, clock source 491 of PCD 400 of FIG. 10 and the voltage supplysource 490 of PCD 400 of FIG. 10 may be implemented in accordance withthe generalized embodiments previously described herein with referenceto FIGS. 1-7.

[0088] As one illustrative example, ADC/mux 342, the RFtransmitter/receiver 336, digital controller timer circuit 332, andvarious other CMOS circuits may be individually operated at differentclock frequencies available from clock source 338. Likewise, suchcircuits may be operated at corresponding supply voltages which may bedifferent for each of the circuits. Further, for example, RFtransmitter/receiver 336 may be operated during a particular time period(e.g., when uplinking) at a particular clock frequency available fromclock source 338 and at a particular supply voltage available fromvoltage supply source 301 corresponding to the particular clockfrequency. On the other hand, during a different time period (e.g.,during downlink), the circuit 336 may be operated at a completelydifferent clock frequency and supply voltage. Automatic adjustment oftelemetry parameters under certain circumstances is described in U.S.Pat. No. 5,683,432 to Goedeke et al.

[0089] Additionally, and in respect of FIG. 10, A/D converter circuit430, cardioverter/defibrillator control circuit 454, and various othercircuits such as RAM 426, DMA 428, and multiplexer 432 may also beoperated at different clock frequencies available from clock source 491and at different corresponding supply voltages available from supplyvoltage source 490. Further, a telemetry circuit (not shown) may be usedwith PCD 400 of FIG. 10 and may also be operated at different clockfrequencies available from clock source 491 and at differentcorresponding supply voltages available from supply voltage source 490.In addition, processor 424 may be operated at different clock speedsdepending upon the function being performed by the processor 424 such asdescribed with reference to FIG. 7 herein. For example, morphologydetection sensing at typical physiologic rates (i.e., 50 to 150 BPM) maybe performed at a first clock frequency and corresponding supply voltagewhile arrhythmia detection may be performed at a different clockfrequency and corresponding supply voltage.

[0090]FIG. 11 shows a variable clock/variable supply voltage digitalsignal processing system 500 which may be used in conjunction withand/or in the alternative to certain circuits shown in FIGS. 9 and 10.For example, the digital signal processing system 500 according to FIG.11 may be used in place of activity circuit 352, pressure circuit 354,sense amplifier circuit 346 (for P-wave, R-wave- and/or T-wave senseamplifiers), and further may be provided with additional functionalitywith use of a pseudo EKG signal 502. Generally, any number of analogsignals 499, for example, such as pseudo EKG signals 502, activitysensor signal 503 and pressure and onset sensor signal 504, are providedthrough respective amplifiers 505-507. The amplified signals arepresented to multiplexer 510 which provides them to analog to digitalconverter (ADC) 516 in a cycled fashion. The signals 502-504 can becycled at different rates by cycling through the outputs of the severalamplifiers/preamplifiers 505-507 such as described in pending U.S.patent application Ser. No. 08/801,335, Medtronic Attorney Docket No.P4521, entitled “Method for Compressing Digitized Cardiac SignalsCombining Lossless Compression and Non-linear Sampling,” which describesvariable compression via ADC sampling and which is incorporated hereinby reference in its entirety. The ADC may also have variable conversionrates as described in U.S. Pat. No. 5,263,486 and U.S. Pat. No.5,312,446 which are also incorporated herein by reference in theirentireties. Input/output interface 514 and program registers 512 areutilized under control of a timing circuit (not shown) to controlapplication of the analog signals from multiplexer 510 to ADC 516 whichprovides such converted digital signals to digital filter 518 to providea waveform for analysis to waveform analysis processor 520 (i.e., adigital signal processor (DSP)). To reduce power, the waveform analysisprocessor 520 is clocked at different speeds, i.e., controlled “on thefly,” according to the present invention, depending upon the processingneeds.

[0091] For example, only during a QRS complex will the waveform analysisprocessor 520 be in a high speed processing mode at a relatively highfrequency, while during the remainder of the cardiac cycle the processor520 may be “idling along” at a much lower clock frequency. Such aprocessing cycle has been previously described with reference to FIG.4C. In addition to the lower clock speed utilized for different portionsof the cardiac cycle, one skilled in the art will recognize that inaccordance with the other aspects of the present invention, as the speedis reduced, the supply voltage level (V_(DD)) may also be reducedaccordingly. Thus, reduced power consumption is attained as previouslydescribed.

[0092] The present invention is compatible with various fabricationtechnologies, including but not limited to, silicon on insulator (SOI),silicon on sapphire (SOS), current mode logic (CML), BICMOS, PMOS andNMOS technologies, as well as conventional silicon CMOS technologies.U.S. Pat. Nos. 4,359.653 to Takamasa; 5,416,043 to Burgener et al.:5,538,908 to Kim; 5,705,421 to Matsushita et al., all herebyincorporated herein by reference, each in its respective entirety,describe integrated circuit fabrication processes and methods of use forat least some of the foregoing integrated circuit types.

[0093] The present invention permits the use of DSPs to perform morefunctions than might otherwise be possible owing to the manner in whichpower consumption may be reduced in such DSPs. Furthermore, multipleprocessor based designs may also be implemented due to reduced powerconsumption as supply voltages and clocking frequencies are reduced forvarious functions performed by the processors.

[0094] Additionally, as power consumption is reduced, furtherfunctionality may be added to devices to provide a device with addedfunctionality relative to previously higher consuming devices. Aprocessor may, for example, perform various morphology detectionfunctions such as differentiation of retrograde P-waves and antegradeP-waves of EGM waveform; differentiation of P-waves from far fieldR-waves; differentiation of AF-A flutter-AT from sinus tachycardia;differentiation of VT-VF-V flutter from SVT; differentiation of cardiacsignals from electromagnetic interference; etc. For example,electromagnetic interference (EMI) may be apparent from theft detectors,conductive signals, RF noise, myopotentials, etc.

[0095] The preceding specific embodiments are illustrative of thepractice of the invention. It is to be understood, therefore, that otherexpedients known to those skilled in the art or disclosed herein may beemployed without departing from the invention or the scope of theappended claims. The present invention is not limited, for example, tothe use of a clock source for providing discrete clock frequencies.Instead, such clock frequencies may be varied in a continuous manner.Moreover, the supply voltage source may include not only discrete supplyvoltages, but may include a source that is varied continuously over aparticular range, such as, for example, by a voltage regulator. Thepresent invention is also not limited to use in conjunction withpacemakers or PCDs, but may find further application in other relevantareas such as telecommunications or portable computers where low powerconsumption is desired. The present invention further includes withinits scope methods of making and using the just-in-time clocking and/ormultiple supply voltage concepts described herein above.

[0096] In the claims, mean plus function clauses are intended to coverthe structures described herein as performing the recited function andtheir equivalents. Means plus function clauses in the claims are notintended to be limited to structural equivalents only, but are alsointended to include structures which function equivalently in theenvironment of the claimed combination.

I claim:
 1. A medical device, comprising: one or more circuits operableto perform at least one function during a predetermined time period,wherein the predetermined time period extends between a prior timeperiod and a subsequent time period, and further wherein at least one ofthe circuits is operable for completing the at least one function in apredetermined number of clock cycles; and a clock source for providingclock signals at a plurality of clock frequencies, the clock sourceoperatively connected to control the at least one circuit at a clockfrequency such that substantially the entire predetermined time periodis used to perform the at least one function, wherein the function iscompleted just prior to the subsequent time period.
 2. The device ofclaim 1, wherein the one or more Circuits comprise at least a firstlogic circuit for performing a first function and a second logic circuitfor performing a second function, wherein the first logic circuit isoperable to perform the first function during a first predetermined timeperiod and the second logic circuit is operable to perform the secondfunction during a second predetermined time period, and further whereineach of the first and second logic circuits is operated at a differentclock frequency such that substantially the entire respective first andsecond predetermined time periods are used by the respective first andsecond logic circuits to perform the respective first and secondfunctions.
 3. The device of claim 2, wherein the first predeterminedtime period and the second predetermined time period are time periodsbased on physiological events.
 4. The device of claim 3, wherein atleast one of the first and second time periods is a time period selectedfrom the following group of time periods associated with cardiac eventsincluding blanking interval, upper rate interval, escape interval,refractory interval, and pulse generator/ programmer handshake.
 5. Thedevice of claim 1, wherein the one or more circuits comprise aprocessing device, the processing device operable to perform a pluralityof functions, each of the plurality of functions being performed duringan associated predetermined time period prior to a subsequent timeperiod in which another of the plurality of functions is performed,wherein the processing device is operable to perform each of two or morefunctions of the plurality of functions at a different clock frequencysuch that substantially the entire associated predetermined time periodfor each function is used to perform the functions prior to thesubsequent time period in which another of the plurality of functions isperformed.
 6. The device of claim 5, wherein the associatedpredetermined time periods are time periods based on physiologicalevents.
 7. The device of claim 6, wherein at least one of the associatedtime periods are time periods selected from the following group of timeperiods associated with cardiac events including blanking interval,upper rate interval, escape interval, refractory interval, and pulsegenerator/ programmer handshake.
 8. The device of claim 1, wherein thedevice further includes one or more supply voltage sources to provideone or more supply voltages, wherein the one or more supply voltagesources are operatively connected to the one or more circuits such thata supply voltage is applied to at least one circuit as a function of theclock frequency applied to the at least one circuit.
 9. The device ofclaim 8, wherein the one or more circuits comprise at least a firstlogic circuit for performing a first function and a second logic circuitfor performing a second function, wherein each of the first and secondlogic circuits is operated at a different clock frequency, and furtherwherein each of the logic circuits has a different supply voltageapplied thereto based on the different clock frequencies used to controlthe first and second logic circuits.
 10. The device of claim 8, whereinthe one or more circuits comprise a processing device, the processingdevice operable to perform a plurality of functions, wherein each of atleast two of the plurality of functions is performed at a differentclock frequency, and further wherein the supply voltage applied to theprocessing device is adjusted such that a first supply voltage is usedfor the processing device during performance of one of the at least twofunctions and a second supply voltage is used for the processing deviceduring performance of the other function, wherein the first and secondsupply voltages are applied based on the different clock frequenciesused to control the processing device.
 11. The device of claim 1,wherein the one or more circuits are of a type selected from the groupconsisting of CMOS circuits, CML circuits. SOS circuits, SOI circuits,BICMOS circuits and NMOS circuits.
 12. The device of claim 1, whereinthe device is an hermetically sealed implantable medical device.
 13. Thedevice of claim 12, wherein the implantable medical device is selectedfrom the group consisting of an implantable stimulator, an implantablenerve stimulator, an implantable pacemaker, an IPG, an implantablecardioverter, an implantable PCD, an implantable defibrillator, animplantable ICD and an implantable drug pump.
 14. A medical device,comprising: a plurality of circuits forming a single integrated circuit,wherein each circuit of the plurality of circuits is operable to performat least one function; and one or more supply voltage sources operableto provide a plurality of different supply voltages, wherein at leastone supply voltage of the plurality of different supply voltages isoperatively connected to at least a first circuit of the plurality ofcircuits, and further wherein at least one different supply voltage isoperatively connected to at least a second circuit of the plurality ofcircuits.
 15. The device of claim 14, wherein the device furtherincludes one or more clock circuits for providing clock signals at aplurality of clock frequencies, and further wherein the clock circuitsare operatively connected to control each of two or more of theplurality of circuits at different clock frequencies.
 16. The device ofclaim 15, wherein the at least one supply voltage of the plurality ofdifferent supply voltages operatively connected to the first circuit isapplied based on the clock frequency used for controlling operation ofthe first circuit, and further wherein the at least one different supplyvoltage operatively connected to the second circuit is applied based onthe clock frequency used for controlling operation of the secondcircuit.
 17. The device of claim 15, wherein a particular circuit of theplurality of circuits performs at least a first and second function andwherein the one or more supply voltage sources operatively connected tothe particular circuit includes: a supply voltage source; and a voltageregulator connected to the supply voltage source, wherein the voltageregulator adjusts the supply voltage source such that a first supplyvoltage applied to the particular circuit for performance of the firstfunction is different than a second supply voltage applied to theparticular circuit for performance of the second function.
 18. Thedevice of claim 17, wherein the first supply voltage and second supplyvoltage are determined based on the clock frequency used to control theparticular circuit during the performance of the first function and theclock frequency used to control the particular circuit during theperformance of the second function, respectively.
 19. The device ofclaim 14, wherein the device further includes means for adjusting theback gate bias of at least one of the first and second circuits based onthe supply voltage applied to the at least one circuit.
 20. The deviceof claim 14, wherein the plurality of circuits are of at least one typeselected from the group consisting of CMOS circuits, CML circuits, SOScircuits, SOI circuits, BICMOS circuits, PMOS circuits and NMOScircuits.
 21. A medical device, comprising: processing circuitry forperforming at least a first and second function; a supply voltage sourceoperatively connected to provide a supply voltage to the processingcircuitry; and a voltage regulator connected to the supply voltagesource to adjust the supply voltage provided to the processing circuitrysuch that a first supply voltage level is applied to the processingcircuitry during performance of the first function and a second supplyvoltage level is applied to the processing circuitry during performanceof the second function, the second supply voltage level being differentfrom the first supply voltage level.
 22. The device of claim 21, whereinthe device further includes an adjustable clock circuit for providingclock signals to control operation of the processing circuitry, andfurther wherein the clock circuit provides clock signals at a firstfrequency for control of the processing circuitry during performance ofthe first function and provides clock signals at a second frequency forcontrol of the processing circuitry during performance of the secondfunction.
 23. The device of claim 22, wherein the first and second levelof the supply voltage are applied based on the first and secondfrequency of the clock signals used for controlling operation ofprocessing circuitry during performance of the first and secondfunctions.
 24. The device of claim 21, wherein the device furtherincludes means for adjusting the back gate bias of the processingcircuitry based on the first and second level of the supply voltageapplied to the processing circuitry.
 25. The device of claim 21, whereinthe first function is performed at a frequency relatively higher thanthe frequency for performing the second function, and further whereinthe second supply voltage level applied during the performance of thefirst function is high relative to the second supply voltage level. 26.The device of claim 25, wherein the first function is a functionselected from the group of high speed telemetry uplink/downlink,morphology detection, device initialization, arrhythmia detection,far-field R-wave detection, EMI detection, and retrograde conduction.27. The device of claim 25, wherein the second function is selected fromthe group of intrinsic heartbeat sensing, pacing, low speed telemetry,transtelephonic data transfer, remote data monitoring, and batterycheck.
 28. The device of claim 21, wherein the device further includes:a multiplexer for receiving a plurality of analog signals; and an analogto digital converter for converting one or more of the analog signals todigital signals and applying such digital signals to the processingcircuitry, wherein the processing circuitry operates on the digitalsignals representative of at least a first analog signal of theplurality of signals to perform the first function and operates on thedigital signals representative of at least a second analog signal of theplurality of signals to perform the second function.
 29. The device ofclaim 21, wherein the processing circuitry is of at least one typeselected from the group consisting of CMOS circuitry, CML circuitry, SOScircuitry, SOI circuitry, BICMOS circuitry, PMOS circuitry and NMOScircuitry.
 30. The device of claim 21, wherein the device is anhermetically sealed implantable medical device.
 31. The device of claim30, wherein the implantable medical device is selected from the groupconsisting of an implantable stimulator, an impiantable nervestimulator, an implantable pacemaker, an IPG, an implantablecardioverter, an implantable PCD, an implantable defibrillator, animplantable ICD and an implantable drug pump.
 32. A method forconserving power for a medical device, the method comprising the stepsof: providing one or more circuits operable to perform at least onefunction during a predetermined time period that extends between a priortime period and a subsequent time period, wherein at least one of thecircuits is operable for completing the at least one function in apredetermined number of clock cycles; and operating the at least onecircuit at a clock frequency such that substantially the entirepredetermined time period is used to perform the at least one function,wherein the function is completed just prior to the subsequent timeperiod.
 33. The method of claim 32, wherein the one or more circuitscomprise at least a first logic circuit for performing a first functionand a second logic circuit for performing a second function, and furtherwherein the operating step includes: operating the first logic circuitto perform the first function during a first predetermined time periodat a first clock frequency such that substantially the entire firstpredetermined time period is used by the first logic circuit to performthe first function; and operating the second logic circuit at a secondclock frequency that is different than the first clock frequency suchthat substantially the entire respective second predetermined timeperiod is used by the second logic circuit to perform the secondfunctions.
 34. The method of claim 33, wherein at least one of the firstpredetermined time period and the second predetermined time period is atime period based on physiological events.
 35. The method of claim 33,wherein the at least one of the first and second predetermined timeperiods are time periods selected from a group of time periodsassociated with cardiac events including blanking interval, upper rateinterval, escape interval, refractory interval, and pulse generator/programmer handshake.
 36. The method of claim 32, wherein the one ormore circuits comprise a processing device, the processing deviceoperable to perform a plurality of functions, each of the plurality offunctions being performed during an associated predetermined time periodprior to a subsequent time period in which another of the plurality offunctions is performed, and further wherein the operating step includes:operating the processing device at a clock frequency to perform at leastone function of the plurality of functions such that substantially theentire associated predetermined time period for the at least onefunction is used to complete the first function prior to a subsequenttime period in which another of the plurality of functions is performed.37. The method of claim 36, wherein the associated predetermined timeperiod is a time period based on physiological events
 38. The method ofclaim 37, wherein the associated time period is a time period selectedfrom a group of time periods associated with cardiac events includingblanking interval, upper rate interval, escape interval, refractoryinterval, and pulse generator/ programmer handshake.
 39. The method ofclaim 32, wherein the method further includes controlling the level of asupply voltage applied to the at least one circuit as a function of theclock frequency.
 40. The device of claim 32, wherein the step ofproviding one or more circuits further comprises the step of providingcircuits of at least one type selected from the group consisting of CMOScircuits, CML circuits, SOS circuits, SOI circuits, BICMOS circuits,PMOS circuits and NMOS circuits.
 41. The method of claim 32, furthercomprising the step of providing an hermetically sealed implantablemedical device.
 42. The method of claim 41, wherein the implantablemedical device providing step further comprises the step of providing animplantable medical device selected from the group consisting of anImplantable stimulator, an implantable nerve stimulator, an implantablepacemaker, an IPG, an implantable cardioverter, an implantable PCD, animplantable defibrillator, an implantable ICD and an implantable drugpump.
 43. A method of conserving power in a medical device, the methodcomprising the steps of: providing a plurality of circuits forming asingle integrated circuit, wherein each circuit of the plurality ofcircuits is operable to perform at least one function; and operating atleast a first circuit of the plurality of circuits at a first supplyvoltage level; and operating at least a second circuit of the pluralityof circuits at a second supply voltage level, wherein the first supplyvoltage level is different than the second supply voltage level.
 44. Themethod of claim 43, wherein the method further includes controlling eachof the first and second circuits with a different clock frequencies. 45.The method of claim 44, wherein the controlling step further includes:determining the first supply voltage level based on a clock frequencyused for controlling operation of the first circuit; and determining thesecond supply voltage level based on a clock frequency used forcontrolling operation of the second circuit.
 46. The method of claim 45,wherein the method further includes adjusting the back gate bias of atleast one of the first and second circuits based on the supply voltagelevel applied to the at least one circuit.
 47. The device of claim 43,wherein the step of providing the plurality of circuits furthercomprises the step of providing circuits of at least one type selectedfrom the group consisting of CMOS circuits, CML circuits, SOS circuits,SOI circuits, BICMOS circuits, PMOS circuits and NMOS circuits.
 48. Themethod of claim 43, further comprising the step of providing anhermetically sealed implantable medical device.
 49. The method of claim48, wherein the implantable medical device providing step furthercomprises the step of providing an implantable medical device selectedfrom the group consisting of an implantable stimulator, an implantablenerve stimulator, an implantable pacemaker, an IPG, an implantablecardioverter, an implantable PCD, an implantable defibrillator, animplantable ICD and an implantable drug pump.
 50. A method of conservingpower in a medical device, the method comprising the steps of: providingprocessing circuitry operable for performing at least a first and secondfunction; operating the processing circuitry at a first supply voltagelevel to perform the first function; and operating the processingcircuitry at a second supply voltage level to perform the secondfunction, wherein the first supply voltage level is different from thesecond supply voltage level.
 51. The method of claim 50, wherein themethod includes: operating the processing circuitry at a first clockfrequency to perform the first function; and operating the processingcircuitry at a second clock frequency to perform the second function,wherein the first clock frequency is different than the second clockfrequency.
 52. The method of claim 51, wherein the step of operating theprocessing circuitry at the first clock frequency and first supplyvoltage level and operating the processing circuitry at the second clockfrequency and the second supply voltage level, include: determining thefirst supply voltage level based on the first clock frequency; anddetermining the second supply voltage level based on the second clockfrequency.
 53. The method of claim 50, wherein the method furtherincludes adjusting the back gate bias of the processing circuitry basedon the first and second supply voltage levels applied to the processingcircuitry.
 54. The method of claim 50, wherein method includes operatingthe processing circuitry to perform the first function at a clockfrequency that is relatively higher than a clock frequency used toperform the second function.
 55. The method of claim 54, wherein thefirst function is a function selected from the group of high speedtelemetry uplink/downlink, morphology detection, device initialization,arrhythmia detection, far-field R-wave detection, EMI detection, andretrograde conduction.
 56. The method of claim 54, wherein the secondfunction is selected from the group of intrinsic heartbeat sensing,pacing, low speed telemetry, transtelephonic data, and battery check.57. The device of claim 50, wherein the step of providing the processingcircuitry further comprises the step of providing circuitry of at leastone type selected from the group consisting of CMOS circuitry, CMLcircuitry, SOS circuitry, SOI circuitry. BICMOS circuitry, PMOScircuitry and NMOS circuitry.
 58. The method of claim 50, furthercomprising the step of providing an hermetically sealed implantablemedical device.
 59. The method of claim 58, wherein the implantablemedical device providing step further comprises the step of providing animplantable medical device selected from the group consisting of animplantable stimulator, an implantable nerve stimulator, an implantablepacemaker, an IPG, an implantable cardioverter, an implantable PCD, animplantable defibrillator, an implantable ICD and an implantable drugpump.